Careful when using the combined attack as it ignores special damages. Say you had a fire sword that gives piercing damage like a sword but fire damage as well. The CombindedAttack will take the values of both the physical and fire and by the code above make all the damage physical. Hence, any creature immune to physical damage would not get damaged. Problem arises when using special abilities with spears and such against banshees.
I had a fix for the impale, crush, and cleave last April,
https://dl.dropboxusercontent.com/u/75549875/Fallen%20Enchantress/Abilities/impalecrushingcleavefix.zip
Your application above needs only remove the
<AttackStat>UnitStat_Attack_Pierce</AttackStat>
and it should create the appropriate damage types correctly. I've not noticed anything different from my fix, but it's hard to say given the random nature of things.
The work around could be to set up an ability called "Can Crit" or something...
The ability would need this game modifier
<GameModifier>
<ModType>Unit</ModType>
</Attribute>MeleeAppliesSpell</Attribute>
<StrVal>CRITSPELL</StrVal>
<Provides>A 10% chance to have a critical attack</Provides>
</GameModifier>
The spell would then utilize
<AppliesRandomModifier>1</AppliesRandomModifier>
Set up 9 different different random modifiers of normal damage. (you can even set it to severely critical something)
Apply the game modifier suggested by Primal (but recall this would be only physical damage, and you would lose the weapons fire, lightning, cold damage, etc.)
**This would be a set-up very close to the gamblers strike.**